Preheat oven to 350 F. Sprinkle chicken breasts with all-purpose seasoning and oil on both sides. In a large skillet over medium-high heat, brown chicken 2–3 minutes on each side. Set aside.

Cut four large pieces of heavy-duty aluminum foil. On each, make a layer of potatoes, then top with a layer of onion slices. Layer green beans along sides. Top vegetables with a chicken breast and 2–3 lemon slices. Break off four sprigs of fresh thyme, and place one on top of lemon in each packet. Fold the foil closed, completely sealing the packet. Place packets on a shallow baking pan, and bake 35–40 minutes. Increase oven temperature to broil. Unfold and open packets, creating a foil bowl, and broil 3–5 minutes, until lemon slices are browned. Remove from oven, and let rest 5–10 minutes before serving in packets.